Abstract

We observe optical trapping and manipulation of dielectric microparticles using autofocusing radially symmetric Airy beams. This is accomplished by exploiting either the inward or outward transverse acceleration associated with their chirped wavefronts. We experimentally demonstrate, for the first time to our knowledge, that such Airy beams morph into nondiffracting Bessel beams in their far-field. Furthermore, the ability of guiding and transporting microparticles along the primary rings of this class of beams is explored.

Generation of autofocusing beam with computer-generated holograms. (a)–(d): Snapshots of the transverse intensity patterns taken at planes as marked by dashed white lines in (e), the side-view of the autofocusing beam propagating along z; (f) typical off-axis hologram.

(a)–(d) Experimental snapshots of transverse intensity patterns of the autofocusing beam (contrast enhanced) taken at different planes as marked in (e), the direct side-view photography of the beam taken from scattered light.

Generation of circular Airy beam with initial outward acceleration. (a)–(d): Intensity snapshots from simulation (first row) and experiment (second row) taken at planes as marked in (e) the side-view propagation along z. Notice that, overall, the beam bends outward rather than inward as seen from the “tails” and the transition into Bessel beam is less abrupt as compared with that in Fig. 2.

Experimental demonstration of particle guidance with a circular autofocusing beam. (a) Illustration of particle motion through a tapered particle guide; (b)–(f) Snapshots of trapped microparticles from videos taken when the particles are trapped at different transverse planes (see Media 1 for an example). Dashed circles serve as a reference while the arrows illustrate the movement of the particles.